Accurate energy eigenvalues for enclosed hydrogen atom within spherical impenetrable boxes

We study the hydrogen atom confined within spherical impenetrable walls. The potential in the box is the Coulombian potential and outside the box the potential is infinite. To compute the energy eigenvalues of the Schrödinger's equation, we use a method proposed few years ago by Campoy and Palma to solve free quantum systems. The energy eigenvalues are computed with great accuracy for different box sizes, in addition we also compute few position expectation values that are related with the hyperfine splitting, nuclear magnetic shielding, polarizability, and pressure. Our results are more accurate than the literature calculations.